I. Field of the Invention
The present invention relates to spread spectrum telecommunications systems. More particularly, the present invention relates to a novel and improved messaging method and apparatus in a CDMA cellular communication system.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes such as amplitude companded single sideband (ACSSB) are known, CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," assigned to the assignee of the present invention and incorporated by reference herein.
In the CDMA cellular system, a large number of mobile telephone system users, each having a transceiver, communicates through satellite repeaters or terrestrial stations which are also referred to as cells. Each cell includes a physical plant called a base station. A cell covers a limited geographic area and routes calls carried over cellular telephones to and from a telecommunication network via a mobile switching center. When a cellular telephone user moves into the geographic area of a new cell, the routing of that user's call may be eventually made through the new cell by a process called a "handoff."
A cellular telephone or, more specifically, a mobile station, broadcasts a signal that is received by a base station. The signal is then relayed to a mobile switching center which in turn routes the signal to the public switched telephone network and to telephone lines or other mobile stations. Similarly, a signal may be transmitted from the public switched telephone network to a mobile station via a base station and a mobile switching center. The communications channel allocated for communication of information between the mobile station and the base station is called the traffic channel.
The interface between the mobile station and the base station is referred to as the Air-Interface. The telecommunications industry association (TIA) has provided a standard for CDMA call processing on the Air-Interface entitled "IS-95-A Mobile Station--Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System," hereinafter IS-95-A, which is incorporated by reference. The interface between the base station and the mobile switching center is referred to as the A-Interface. The TIA has provided for call processing on the A-Interface through the standard provided in "IS-634 Mobile Switching Center--Base Station Interface for Public 800 MHz," which is also incorporated by reference. IS-95-A and IS-634 both define the messages and signals that are sent on their respective interfaces for the operation of a CDMA cellular telephone call.
The call flow in a CDMA environment requires processing on both the Air-Interface and the A-Interface. The successful progression of a call requires that the proper messages and signals are sent at the right times on both the Air-Interface and the A-Interface. The IS-634 standard is being developed to provide for call processing on the A-Interface. A number of problems and deficiencies are present in IS-634 which currently does not support some of the necessary operations on the A-Interface. Some of these problems and deficiencies are recognized and solved by the present invention in the manner described below.